Mitsubishi Electric MELSEC iQ-RJ71EN71 User Manual page 232

■When the control system IP address is not used
When the control system IP address is not used, access the control system CPU module by using the following procedure.
1.
Execute the open processing in the order system A  B.
2.
Read 'Control system judgment flag' (SM1634) and 'Standby system judgment flag' (SM1635) to judge the control
system.
3.
Specify the control system CPU module for the request destination module I/O number and send a command message.
4.
Check the response message.
To continue the communication, send command messages continuously.
5.
Execute the close processing in the order the control system  the standby system.
Communications using the predefined protocol
When the control system IP address is not used, establish the connection with the Ethernet-equipped modules of both
systems and perform communications. When only sending data from the external device to the Ethernet-equipped module,
send the data to the Ethernet-equipped modules of both the control and standby systems because the system switching
timing is not able to be ascertained.
Socket communications
■Receive processing by the standby system
If data is sent to the standby system Ethernet-equipped module, data reception processing will not be performed because the
module reads and discards the received data.
■Receive processing with interrupt program
If system switching occurs before execution with the interrupt program, and the control system is switched to the standby
system, the interrupt factor will not be transferred to the other system. The interrupt factor will be retained on the own system.
Therefore, if system switching occurs again and the own system becomes the control system, the interrupt program will be
executed by the retained interrupt factor.
■When data is sent from an external device
• When the control system IP address is not used, the system switching timing is not able to be ascertained. Send data to the
Ethernet-equipped modules of both the control and standby systems.
• To use the control system IP address, check whether the Ethernet-equipped module is alive from the external device side.
1 FUNCTIONS
230
1.17 Redundant System Function